A dog enjoys the living room of a custom home in Belvedere, which finally has a likely buyer for more than $25 million.

Photo: David Paul Morris, Bloomberg

A dog enjoys the living room of a custom home in Belvedere, which...

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The Golden Gate Bridge is seen in the view from the 15,000-square-foot, custom-built Belvedere home.

Photo: David Paul Morris, Bloomberg

The Golden Gate Bridge is seen in the view from the...

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The pool area of a 15,000 square-foot custom built home lies in shadows on Belvedere Island in Marin County, California, U.S., on Wednesday, Dec. 19, 2012. The builder couldn't find a buyer for the brand-new waterfront mansion he listed in January for $45 million. He hopes one will turn up at a Dec. 30 auction, where the starting bid will be $25 million. Photographer: David Paul Morris/Bloomberg

Photo: David Paul Morris, Bloomberg

The pool area of a 15,000 square-foot custom built home lies in...

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Zynga fortunes went up and down this year, but seems the Pincus family mostly landed on top, purchasing this Pac Heights home for $16 million in July of 2012. Photos via SF Gate/SFMLS.

Zynga fortunes went up and down this year, but seems the Pincus...

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130 Seacliff sold for $13 million this year, a 5 bed, 7.5 bath ocean view luxury home of over 6,000 square feet. Photo via CurbedSF.

For months, Jeff Paster, a developer of luxury homes in Marin County, couldn't find a buyer for the brand-new Belvedere waterfront mansion he listed in January for $45 million. So he put it up for auction Sunday, but then canceled it when a mystery buyer stepped forward with an undisclosed offer - somewhere north of $25 million - at the last minute.

"People at this income level," Paster said before the auction that wasn't, "always have money."

That maxim proved true when it came to luxury properties in the Bay Area last year. Technology executives paying discounts on listed prices were active buyers in 2012, as the growth of social-media and Internet firms including Twitter and Yammer created a wave of millionaires.

Some older homes on the market had sat unsold for years before finding buyers, said Rick Turley, president of Coldwell Banker Residential Brokerage of Northern California. But by the final week of 2012, there were at least 13 publicly recorded transactions for more than $10 million in exclusive San Francisco neighborhoods such as Pacific Heights, Presidio Heights and Sea Cliff, according to DataQuick, a research firm.

That's up from six sales last year and a dozen in 2007, the previous high mark. The numbers don't include deals in expensive areas outside the city, such as Belvedere, Tiburon, Atherton or Palo Alto.

"Over a long listing period, it's hard to say what will happen, because obviously the market is constantly changing," Turley said. "The success of tech and social media means people are looking very generally at San Francisco and the Silicon Valley as places to live because these businesses are sourced here. It's highest on their radar."

Initial public offerings in 2012 by Bay Area companies raised a record $17.5 billion in public equities markets, including sales by Facebook, Yelp and Workday, according to data compiled by Bloomberg. The total is more than double the $8.3 billion reached in 1999, the height of the dot-com boom.

This year's Bay Area IPOs generated $9.4 billion in cash for selling shareholders. Other investors have been able to generate money before initial stock sales through the rise of secondary-share markets such as SharesPost.

Yammer founder

Yammer founder David Sacks, who sold the social-media company to Microsoft in June for $1.2 billion, later bought an unfinished home in Pacific Heights that had been listed for $38.5 million. The transfer tax indicated a $20 million sale.

"It's built to be the finest residence in San Francisco, from limestone quarried in France and with the same glaziers who worked on the Eiffel Tower renovation," Barrett said.

In December, Jay Paul, the San Francisco developer of 6 million square feet of Silicon Valley offices, including Google's four-building complex in Sunnyvale, completed a purchase in the same neighborhood, said a person with knowledge of the transaction. The house sold for $28.25 million, said Dona Crowder of TRI Coldwell Banker, a co-listing broker on the home. She declined to comment on the buyer.

Seller deals

The deal was at a 48 percent discount from the asking price in 2007, around the time U.S. housing prices peaked. The seller had most recently sought $34 million, Crowder said.

Paul didn't return a telephone message seeking comment.

In some cases, luxury discounts this past year in San Francisco and the Silicon Valley are a reflection of aged homes built decades ago that needed extensive renovations, Crowder said. Sellers were also motivated by the prospect of higher capital gains taxes in 2013, she said. Her listing on Broadway in Pacific Heights received higher bids in the past, including one earlier in 2012, which were rejected by the seller, she said.

"The generations are turning over in this neighborhood," Crowder said in a phone interview. "If it were understood back then that record prices were being offered, it would have been wise to sell" in 2007.

Dorsey, Benioff

Jack Dorsey, a Twitter co-founder, paid $9.9 million in February for a "humble" two-bedroom house in Sea Cliff that had been listed for $12.5 million, said Olivia Hsu Decker, owner of Tiburon's Decker Bullock Sotheby's International Realty and Dorsey's agent on the deal. Salesforce.com CEO Marc Benioff bought a nearby house in 2009, Decker said.

The Sea Cliff neighborhood is named for its location high above the Pacific Ocean, just west of the Golden Gate. In May, Dorsey, who is known to take public buses to work, tweeted a quote from the Chilean poet Pablo Neruda, "I need the sea because it teaches me," Decker said.

Other multimillion-dollar home buyers of 2012 included Mark Pincus, founder of online game maker Zynga. He purchased a Pacific Heights house in July for $16 million after a $500,000 price cut, said Decker, who represented him in the past and also was the listing agent for the Belvedere home.

Rising prices

The region's broader housing market is also showing strong demand, bolstered by the addition of 32,400 new jobs in the San Francisco metropolitan area in the year through November. House and condominium prices in the nine-county Bay Area in November rose almost 21 percent from a year earlier to a median $438,000, the highest since August 2008, according to DataQuick of San Diego. Sales jumped almost 16 percent.